Aromatic polyethers are important engineering resins because of their excellent properties such as high temperature resistance, good electrical properties, good chemical and solvent resistance and toughness.
Poly(aryl ether)s with high heat resistance, low level of cyclic oligomers, and narrow polydispersivity are highly desirable for manufacturing of molded articles for demanding automotive, aerospace and electronics applications.
One route to the synthesis of these polymers is by the reaction of salts of dihydroxyaromatic compounds, such as bisphenol A, with activated dihaloaromatic molecules. One commercially available group of poly(aryl ether sulfone)s, available from Solvay Advanced Polymers LLC, under the trade-mark Radel®, are those containing a biphenyl moiety, typically derived from 4,4′-biphenol. Poly(aryl ether sulfone)s are conventionally made by the nucleophilic polycondensation of 4,4′-biphenol with bis(4-chlorophenyl)sulfone as described, for example, in U.S. Pat. Nos. 4,108,837, 4,175,175, and 6,228,970. Due to their excellent mechanical and other properties, poly(biphenyl ether sulfone)s can be used to manufacture a variety of useful articles such as molded articles, films, sheets and fibers. However, the glass transition temperature (Tg) of the poly(biphenyl ether sulfone) is 220° C., and cannot be used in applications where heat resistance of greater than 220° C. is required.
U.S. Pat. No. 5,254,663 teaches a new class of poly(aryl ether)s containing the phthalazinone moiety. This new class of polymers has also been described extensively in the literature [1-9]. Poly(aryl ether sulfone) containing the phthalazinone moiety, also called poly(phthalazinone ether sulfone), has the structure 1 and has a glass transition temperature (Tg) of about 305° C., is suitably made by the nucleophilic polycondensation of 4(4-hydroxyphenyl)-1(2H)-phthalazinone (called phthalazinone monomer or DHPZ herein and having the structure 2) with bis(4-chlorophenyl)sulfone in a polar solvent in the presence of potassium carbonate.

The poly(phthalazinone ether sulfone)s produced contain a high level of cyclic oligomers, typically 12-18%, by weight, and have very high polydispersivity, typically 10 to 16. A high level of cyclic oligomers has adverse effects on the properties of the resulting polymers. Such negative effects can include a lower Tg, reduced solubility in solvents, and reduced ductility. The high levels of cyclic oligomers have to be removed by tedious steps of re-precipitation in order to produce useful products. In addition, the cyclic by-products must be discarded after separation, increasing the cost and size of the waste stream and reducing the efficiency of the process.
Poly(phthalazinone ether sulfone)s are high Tg amorphous polymers and offer potential as high temperature resistance resins. Poly(phthalazinone ether sulfone)s can be prepared via the nucleophilic polycondensation reaction of the phthalazinone-containing monomer 4-(4-hydroxyphenyl)phthalazin-1(2H)-one with activated dihaloaromatic molecules. Due to the unique chemical structure of the phthalazinone moiety, it is prone to formation of a high level of cyclic oligomers during the nucleophilic polycondensation reaction. These low molecular weight cyclic oligomers have negative effects on properties and are undesirable. In addition, due to extremely high melt viscosity, the existing material cannot be processed using conventional melt processes such as extrusion and injection molding.
The homopolymer prepared from DHPZ and bis(4-chlorophenyl)sulphone has a very high Tg, about 305° C., and cannot be melt processed since at the very high temperatures that would be required, significant degradation would occur. Meng, Hay et al attempted to improve the melt processability of poly(phthalazinone ether sulfone) through copolymerization with 4,4′-difluorobenzophenone to make poly(phthalazinone ether sulfone ketone) (PPESK) [6, 8]. The ketone homopolymer has a Tg of about 265° C. and therefore the ketone/sulfone copolymers have Tg values between the Tg of the two homopolymers, i.e., 265° C. to 305° C. However, these polymers were also not melt processable because of their high melt viscosities. The melt viscosity of poly(phthalazinone ether sulfone ketone) with a relatively low molecular weight (inherent viscosity of 0.29 dL/g) is still very high and it cannot be used for injection molding [6]. In order to have injection moldable resins, the copolymer had to be blended with low molecular weight oligomers of poly(aryl ether sulfone) or poly(phthalazinone ether sulfone) [6]; or to be blended with liquid crystal polyester (LCP) that resulted in an immiscible blend [8]. Since the LCP is immiscible, these blends are not transparent, and the Tgs of the blends still show the PPESK glass transition, although it is slightly lowered.
Another approach that was studied was the preparation of copolymers with hydroquinone (PAES 1), bisphenol-A (BPA) (PAES2), and bis(4-hydroxyphenyl) sulfone (PAES 3) [7]. These polymers were synthesized in order to lower the melt viscosity so that the polymers could be potentially melt processed. A PAES 3 polymer containing 65% DHPZ has a high Tg but also a very high melt viscosity that makes it unprocessable. PAES 2 with contents as high as 80% DHPZ have improved melt viscosities; however, the Tg is only 258° C. at 80% DHPZ. The PAE 1 polymers would not be expected to have high temperature capabilities and a 50:50 copolymer had a Tg of 242° C. Copolymerization with hydroquinone, BPA or bis(4-hydroxyphenyl)sulfone can produce copoly(phthalazinone ether sulfone)s with reduced melt viscosity; however, a copoly(phthalazinone ether sulfone) with phthalazinone as minor component (e.g. 25 mol %) still has very high melt viscosity (˜105 Pa·s), and materials with good mechanical properties from these copolymers were only obtained from samples prepared via solution casting [7].
